## Lithium Ion Battery

Lithium Ion Batteries find wide application in mobile phones and other electronic devices.  In Lithium ion batteries, Lithium metallic oxide is the anode while carbon is used as the negative electrode.  Lithium ions are transferred between the lithium oxide anode and the carbon electrode during charging and in the opposite direction while discharging.

The higher power density and the high voltage per cell (3.6 V) ensures that a single battery can be used.   Lithium Battery can hold charge more effectively than other batteries.  A typical lithium battery loses 5% of its energy every month.

Lithium ion battery packs typically have a small in built electronic control device which continually monitors the temperature, voltage and current.  It shuts down the battery when there is a deviation from established limits.

Lithium Ion batteries are extremely sensitive to temperature and can degenerate faster.  The Lithium battery should never be completely discharged. If that happens the chip which controls the battery will no longer be powered.  The battery cannot be used again.

There have been rare cases when lithium ion batteries catch fire.  This is mostly due to defects in the manufacturing process.

## The Output Equation of a DC machine

The output equation of a DC machine describes the power of the DC machine in terms of its dimensions.  In this post, we will try to derive the equation.

## What is the speed of Electricity ?

This is a question we come across often.  The speed of any electromagnetic wave depends on the medium.  In Vacuum, the speed of an electromagnetic wave will almost approach the speed of light.  However, in actual power transmission, the speed of electricity is lesser than the speed of light.  The speed depends on what is known as the velocity constant.  This depends on the resistance, inductance and the capacitance of the transmission line.  Of these, the capacitance is the primary quantity which determines the speed of electricity through the system.

For instance, in cables, the speed of electricity is dependant on the capacitance of the cables.

The velocity constant of a transmission line is given by VF = 1/k where k is the dielectric constant of the material through which the electromagnetic signal passes.

## Duty Cycles of Welding Machines

The duty Cycle of a welding machine is specified in percentage of 10 minutes.  For instance, if a welding machine is designated as 60%, it means that it can be used continuously for 6 minutes in a 10 minute period and should be rested for the remaining 4 minutes.

The duty cycle of a welding machine depends on its current capacity.  In general, most welding machines will have a duty cycle of 60%.  The duty cycle is also known as the Operation Factor.

## FerroFluids

Ferrous Fluid is a viscous liquid which is magnetic.  Ferrous Fluids are made by mixing minute iron particles whose size is of the order of nanoamperes with a viscous fluid like oil. The particles which constitute the ferrofluid are less than 10 nanometers in size.   This results in a colloidal solution.    A surfactant such as oleic acid or citric acid is applied to the filings to prevent clumping.  When the ferrous fluid is exposed to a magnetic field.

When the ferrofluid is exposed to a magnetic field, it gets magnetized and assumes a range of geometric patterns depending on the magnetic lines of force.  The pattern assume the form of  corrugations due to the effects of gravity and surface tension on the liquid mass.

FerroFluids find wide application in liquid seals, high end speakers and computer disk drives.